opencv/modules/imgcodecs/src/ios_conversions.mm

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#import <UIKit/UIKit.h>
#import <Accelerate/Accelerate.h>
#import <AVFoundation/AVFoundation.h>
#import <ImageIO/ImageIO.h>
#include "opencv2/core.hpp"
#include "precomp.hpp"

CV_EXPORTS UIImage* MatToUIImage(const cv::Mat& image);
CV_EXPORTS void UIImageToMat(const UIImage* image, cv::Mat& m, bool alphaExist);

UIImage* MatToUIImage(const cv::Mat& image) {

    NSData *data = [NSData dataWithBytes:image.data
                                  length:image.step.p[0] * image.rows];

    CGColorSpaceRef colorSpace;

    if (image.elemSize() == 1) {
        colorSpace = CGColorSpaceCreateDeviceGray();
    } else {
        colorSpace = CGColorSpaceCreateDeviceRGB();
    }

    CGDataProviderRef provider =
            CGDataProviderCreateWithCFData((__bridge CFDataRef)data);

    // Preserve alpha transparency, if exists
    bool alpha = image.channels() == 4;
    CGBitmapInfo bitmapInfo = (alpha ? kCGImageAlphaLast : kCGImageAlphaNone) | kCGBitmapByteOrderDefault;

    // Creating CGImage from cv::Mat
    CGImageRef imageRef = CGImageCreate(image.cols,
                                        image.rows,
                                        8 * image.elemSize1(),
                                        8 * image.elemSize(),
                                        image.step.p[0],
                                        colorSpace,
                                        bitmapInfo,
                                        provider,
                                        NULL,
                                        false,
                                        kCGRenderingIntentDefault
                                        );


    // Getting UIImage from CGImage
    UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);

    return finalImage;
}

void UIImageToMat(const UIImage* image,
                         cv::Mat& m, bool alphaExist) {
    CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
    CGFloat cols = CGImageGetWidth(image.CGImage), rows = CGImageGetHeight(image.CGImage);
    CGContextRef contextRef;
    CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast;
    if (CGColorSpaceGetModel(colorSpace) == kCGColorSpaceModelMonochrome)
    {
        m.create(rows, cols, CV_8UC1); // 8 bits per component, 1 channel
        bitmapInfo = kCGImageAlphaNone;
        if (!alphaExist)
            bitmapInfo = kCGImageAlphaNone;
        else
            m = cv::Scalar(0);
        contextRef = CGBitmapContextCreate(m.data, m.cols, m.rows, 8,
                                           m.step[0], colorSpace,
                                           bitmapInfo);
    }
    else if (CGColorSpaceGetModel(colorSpace) == kCGColorSpaceModelIndexed)
    {
        // CGBitmapContextCreate() does not support indexed color spaces.
        colorSpace = CGColorSpaceCreateDeviceRGB();
        m.create(rows, cols, CV_8UC4); // 8 bits per component, 4 channels
        if (!alphaExist)
            bitmapInfo = kCGImageAlphaNoneSkipLast |
                                kCGBitmapByteOrderDefault;
        else
            m = cv::Scalar(0);
        contextRef = CGBitmapContextCreate(m.data, m.cols, m.rows, 8,
                                           m.step[0], colorSpace,
                                           bitmapInfo);
        CGColorSpaceRelease(colorSpace);
    }
    else
    {
        m.create(rows, cols, CV_8UC4); // 8 bits per component, 4 channels
        if (!alphaExist)
            bitmapInfo = kCGImageAlphaNoneSkipLast |
                                kCGBitmapByteOrderDefault;
        else
            m = cv::Scalar(0);
        contextRef = CGBitmapContextCreate(m.data, m.cols, m.rows, 8,
                                           m.step[0], colorSpace,
                                           bitmapInfo);
    }
    CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows),
                       image.CGImage);
    CGContextRelease(contextRef);
}